A known electrical medium-voltage or high-voltage switchgear assembly includes at least one circuit breaker for opening an electrical connection between two switch poles of an electrical phase during operation of the switchgear assembly, and at least one switching device per electrical phase. The term switching device is understood below to mean grounding switches, switch disconnectors or combined disconnector and grounding switches, in which opening of an electrical connection is performed by a movement of a switching element from a first position into another, second position between two switch poles of an electrical phase of the switching device, usually not during nominal operation of the switchgear assembly.
In the case of many such switching devices, a drive device for moving the movable switching element is arranged on the switch housing or even integrated therein. As a result, in a known switchgear assembly, the switching devices are firstly arranged locally sometimes far apart from one another and are secondly aligned, where possible, differently still relative to one another in three dimensions.
In addition to various specifications such as compliance with the relevant regulations, for example, the IEC Standard 62271-102:2003, customer specifications are also to be met which demand, for example, that the switching position of the switching device is indicated visually to an operator at any time by means of a switching position indication. This is often the case, for example in the case of gas-insulated switchgear assemblies, and in particular results in a complex monitoring procedure, in particular in the case of switchgear assemblies requiring a large amount of space, when a plurality of switching positions need to be monitored visually by an operator. Assemblies are known in which this problem is solved via an electronic switching position indication, whereby an input drive shaft position corresponding to a predetermined switching element position is communicated electronically to a display close to the user. However, this second solution does not meet the customer specification for an uninterrupted mechanical chain between the switching element and the switching position indication. Moreover, in the event of a fault, for example in the event of failure of the secondary current system, the operator is no longer provided with any more information on the switching state, such as the switching position of the movable switching elements of the switches relative to the switching poles. This is typically not tolerated by the operator of a switchgear assembly since the indication of the switching position of electrical devices represents a safety-relevant criterion.
One possible way of improving the situation consists in the switching element being moved from a location remote from the actual switch via a flexible shaft.
U.S. Pat. No. 5,466,902 has disclosed a switching apparatus in which a movable switching element of a switching device is fixedly connected to a switching lever via a flexible shaft, with the result that the switching element can be operated by a switching lever from an operating region with a remote location from the switching device. The switching lever is fixedly connected to a rotatable input section of the flexible shaft, and the switching element is fixedly connected on the output-drive side to one rotatable output section, with the result that the movable switching element can be moved over from a first position into a second position.
The inclusion of a flexible makes it possible to overcome, in a structurally simple manner, mass and position tolerances between the input section and the output section and, thanks to the different orientability or alignability of the input section and the output section, contributes to considerable design freedom.
With the flexible shaft, however, as the switching element leaves the first position, for example, when a greater use of force on the switching lever is required than when the switching element is moved merely between the first and the second position. This greater use of force results from an adhering effect of contact elements, which may be arranged on the movable part of the nominal contact transition. As the use of force increases, a rotary angle shift, which can be generated by a first rotary angle of the flexible shaft at the output section and a second rotary angle at the input section at the same time, becomes greater. If torque is now introduced into the switching lever, it may arise, depending on the torsional strength of the flexible shaft, that, when the first position of the switching element is left, the switching lever is already in a position which corresponds to a switching position of the switching element between the first and second positions, while the switching element, from an electrical point of view, is still in the first position. Since the operator of a switching device always needs to know, simply for safety reasons, whether a switching element is still located in a certain electrical position or not, such a state is unfavorable, if not completely insupportable.
Depending on the embodiment of the switching device, the drive torque for the movable switching elements of such switching devices is approximately 10 Nm, for example. Depending on the embodiment of the flexible shaft, a rotary angle shift between the input section and the output section during the introduction of a torque of a few Newton meters at the input section can suddenly be greater than 30° (degrees), for example, 60° or even greater, at a length of the flexible shaft of approximately 2 meters. As the length of the flexible shaft increases, the rotary angle shift increases. This is associated with the uncertainty as to whether the switching element is now already in the desired switching state or whether it is still in one switching position during the preceding switching state. This lack of certainty is insupportable both technically and in terms of safety.